1. Field of the Invention
The present invention relates to valve stem seals, and more particularly to a two-piece valve stem seal for use in intake and exhaust manifolds of an internal combustion engine.
2. Description of Related Art
Valve stem seals are known in the art as shown in U.S. Pat. Nos. 4,947,811; 4,909,202; 3,554,562; and 3,554,180. The valve stem seals are used to keep oil from being drawn into the combustion chamber or into the exhaust manifold from around the valve stem. If leakage is allowed to occur an increase in oil consumption of the vehicle and an impairment of proper engine performance as specified by manufacturers will result.
Generally speaking a valve stem seal assembly includes a rigid shell to secure a seal body on a valve stem guide, with the inside diameter of the shell engaging the outside diameter of the guide. The shell usually supports a sealing element which is centered about the valve stem in order to meter the oil that lubricates the guide inner diameter valve stem interface yet limit oil or liquid from being drawn into a combustion chamber or exhaust chamber. If the rigid shell is not properly placed in relation to the valve guide the sealing element might not properly seat upon the valve stem thus causing non-uniform pressures at the cylinder and valve guide, undesirable wear patterns on the seal or valve stem and unpredictable oil control for the valve stem.
U.S. Pat. No. 4,947,811 uses a garter spring to secure the rubberized seal member around the valve stem. This design is insufficient because the garter spring can dislodge or pop off during installation or over usage. With the spring missing there is no longer compression force on the valve stem thus reducing the effectiveness of the seal. The use of this garter spring also increases the weight and production costs of such a valve guide system.
Other designs of current valve stem seals are disadvantaged by the high assembly load used in metal-to-metal press fittings. This increases the cost of assembling the valve guide system.
Therefore, there is a need in the art for a valve stem seal to overcome the many disadvantages of the prior art.